Referring to FIG. 7, a conventional bicycle hub apparatus comprises a hub body (40), a sleeve (50) and a driving unit (60). A hub axle (41) axially penetrates through the hub body (40). A connecting space (42) is formed at an end of the hub body (40), and an annular connecting unit (43) is installed inside the connecting space (42). A plurality of first ratchet teeth (431) are formed in sequence at an inner periphery of the connecting unit (43). The sleeve (50) is a hollow cylinder and has an open end (51) at an end thereof, and a plurality of second ratchet teeth (511) is sequentially formed at an inner periphery of the open end (51). The sleeve (50) is connected to the connecting space (42) through the open end (51), and the hub axle (41) of the hub body (40) penetrates through the sleeve (50). The driving unit (60) comprises two elastic members (61), a first ratchet ring (62) and a second ratchet ring (63), and the two elastic members (61) are spiral springs respectively disposed on the connecting space (42) of the hub body (40) and an interior space of the open end (51) of the sleeve (50). A plurality of first engaging teeth (621) and a plurality of second engaging teeth (631) are respectively formed at an outer periphery of the first ratchet ring (62) and an outer periphery of the second ratchet ring (63). The first ratchet ring (62) is configured to be coupled with the second ratchet ring (63), and a plurality of first coupling teeth (622) formed at a first surface of the first ratchet ring (62) is adapted to engage with a plurality of second coupling teeth (632) formed at a surface of the second ratchet ring (63) which is coupled with the first surface of the first ratchet ring (62). The first ratchet ring (62) is installed inside the connecting space (42) of the hub body (40), and the first engaging teeth (621) are engaged with the first ratchet teeth (431) of the connecting unit (43). Moreover, the second ratchet ring (63) is arranged inside the interior space of the open end (51) of the sleeve (50), and the second engaging teeth (631) are engaged with the second ratchet teeth (511). In addition, the two elastic members (61) respectively bear against the first ratchet ring (62) and the second ratchet ring (63) to enable the first coupling teeth (622) and the second coupling teeth (632) to be engaged and moved concurrently.
When a freewheel drives the sleeve (50) to turn in a forward direction, referring to FIG. 8, the second ratchet ring (63) is turned and the second coupling teeth (632) is configured to engage with the first coupling teeth (622) of the first ratchet ring (62). Thus, the first ratchet ring (62) and the hub body (40) are driven and turned concurrently in the forward direction. On the other hand, when the freewheel drives the sleeve (50) to have rotation in a reverse direction, referring to FIG. 9, the second coupling teeth (632) is disengaged from the first coupling teeth (622) and the two elastic members (61) are respectively to be compressed to detach the second ratchet ring (63) from the first ratchet ring (62), thereby leaving the sleeve (20) to have rotation independently.
However, the conventional bicycle hub apparatus is disadvantageous because: (i) the first ratchet ring (62) is engaged with the second ratchet ring (63) through the elastic members (61), which increases the manufacturing complexity and cost, and during the moving, the elastic members (61) may be compressed by the first ratchet ring (62) and the second ratchet ring (63) to lead to an unstable engagement; and (ii) the elastic members (61) are spiral springs, which cannot be evenly attached on surfaces of the first ratchet ring (62) and the second ratchet ring (63). As a result, the uneven forces are acted on the first ratchet ring (62) and the second ratchet ring (63), which leads to the engaging loose between the first coupling teeth (622) and the second coupling teeth (632). Therefore, there remains a need for a new and improved design for a bicycle hub apparatus to overcome the problems presented above.